Method for filtering benzene from a gas stream

ABSTRACT

The present invention relates to a method of filtering, at the end user&#39;s home, business or the like, a gas stream in which benzene has been concentrated at sufficient levels to be a significant health hazard. Steps of the invention include: 
     (a) introducing the natural gas stream to a filter selected from a group that includes at least activated charcoal and impingement adsorbing media whereby benzene concentrated in the gas stream at sufficient levels to be a health threat by aperiodic loading of such network in which benzene become clumped into packets due to dampening effects of the compressor-driven equipment and multiple customer outlet usage coupled with surprising longivity of the in situ benzene, is filtered from the gas stream and captured irrespective of mode of transport, 
     (b) passing the filtered natural gas stream to the customer&#39;s gas appliance wherein safe use of the energy associated with the stream occurs, 
     (c) periodically and safely removing the filter of step (a) for disposing of captured benzene, 
     (d) inserting a new filter in place of the removed filter of step (c).

SCOPE OF THE INVENION

The present invention relates to a method of filtering. Moreparticularly, it relates to a filtering method to eliminate benzene thathad been concentrated within a conventional gas line network atsufficient levels to be a health threat. As a further constraint, thesources of such benzene concentration are identified. It is believedthey result from aperiodic loading of such network in which benzenebecome clumped into packets due to dampening effects of the compressordriven network and multiple customer outlet usage that adds theaforementioned aperiodic loading within the network.

DEFINITIONS

In this Application, "natural gas" means a mixture of gases associatedwith hydrocarbon accumulation within the earth as well as processed fuelgases derived from petroleum as well as mineral products such as coal ineither gas or liquid phases. In some gas line networks, the resultingfinal gases may be a mixture from these two sources but wherein theessential component consists of methane.

"Sufficient level to be a health threat" means a recognized standard forhuman health and safety established by authoritative bodies above whichcancer or reproductive toxicity in humans results, such bodies toinclude but not be limited to the U.S. Environmental Protection Agency(EPA), the U.S. Department of Food and Drug Administration (FDA) and theU.S. Department of Commerce. The EPA has set health and safety standardsfor radon which, if exceeded, would pose a risk to human health.

"Adsorption" means filter media that captures molecules of a gas, liquidor dissolved substance to the filer surface, by adhesion.

"Absorption" means filter media that absorbs molecules of a gas, liquidor dissolved substance to the filter itself, by taking in through poresor interstices.

"Impingement" means filter media that captures molecules of a gas,liquid, solid or a dissolved substance to the filter by physical capturesuch as by change in velocity.

BACKGROUND OF THE INVENTION

The danger of benzene is well documented. Benzene concentration levelsat a customer-end user's home, business and the like are not monitored,however. Believed to cause cancer, skin and organ damage and bone marrowdepression, benzene has acute penetration efficiency and once within ahuman's body, does not dissipate and builds a significant body burden asa function of frequency and level of exposure. While the EPA and variousState Agencies may be aware of the problem of benzene in gas lines (from10 to 20 ppm by reports), they do not think the reported exposure is ofsufficient levels to be dangerous.

In such situation, I find that surprisingly large concentrations ofbenzene sporadically occur. Sources of such concentration: dampeningeffects of the compressor-driven network and multiple customer outletusage that add to aperiodic loading of the natural gas stream coupledwith surprising longevity of the in situ benzene. As a result, benzenecan flow to appliances in the customer's home, business or the like atsufficient levels to be a health hazard, i.e. exceed Federal and/orState health and safety standards. Moreover, although the originalsource of the benzene is in the gas phase, both liquid and gaseous formscan be transported alone or attach to particulates and form the finalend-use contamination levels at the appliance to be used.

SUMMARY OF THE INVENTION

The present invention relates to a method of filtering, adjacent to theend user's home. business or the like such as the adjacent gasdistribution and processing system connected to the end user's meter, agas stream in which benzene has been concentrated at sufficient levelsto be a significant health hazard. Steps of the invention include: (a)introducing the natural gas stream to a filter selected from a groupthat includes at least activated charcoal and impingement adsorbing andabsorbing media whereby benzene concentrated in the gas stream atsufficient levels to be a health threat by aperiodic loading of suchnetwork in which benzene become clumped into packets due to dampeningeffects of the compressor-driven equipment and multiple customer outletusage that add to aperiodic loading of the natural gas stream coupledwith surprising longevity of the in situ benzene, is filtered from thegas stream and captured, (b) passing the filtered natural gas stream tothe customer's gas appliance wherein safe use of the energy associatedwith the stream occurs, (c) periodically and safely removing the filterof step (a) for disposing of the captured benzene, (d) inserting a newfilter in place of the removed filter of step (c).

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a gas valve-meter assembly attached at oneend to a pipe of a gas line network adjacent to a home, business or thelike, along with a filtering assembly and by-pass network of the presentinvention;

FIG. 2 is a top view of the filtering assembly of the invention;

FIG. 3 is a section taken along lines 3--3 of FIG. 2;

FIG. 4 is an enlarged detail view taken along lines 4--4 of FIG. 3;

FIG. 5 is an enlarged detail of the filter media unit of FIG. 3;

FIG. 6 is an enlarged detail of an insert ring used in the filter mediaunit of FIG. 3; and

FIG. 7 is an alternate design for the filter unit of FIG. 5.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a gas meter 10 connected via elbow 11 and gas pipe 12to a main gas line network (not shown). Downstream of the meter 10 is atee coupler 14 having a first end 15 connected to an overhead by-passnetwork generally indicated at 16, and a second end 17 connected througha first valve 18 and inlet fitting 19 to filter assembly 20. The filterassembly 20 in turn connects via outlet fitting 40, elbow 41 and asecond valve 42 to the overhead by-pass network 16. As shown, theby-pass network 16 includes a parallel by-pass valve 43. In operation,the by-pass valve 43 operates in complementary fashion with respect tofirst and second valves 18 and 42, respectively. When valve 43 isclosed, as shown, the valves 18 and 42 are open and the filter assembly20 is in operation. When valve 43 is open, the valves 18 and 42 areclosed and the filter assembly 20 is in a deactivated state.

FIGS. 2, 3 and 4 show the filter assembly 20 in more detail.

As shown, the filter assembly 20 includes a cap 21 fitted with arectangularly cross-sectioned dome 22 at its upper surface 21a, seeFIGS. 2 and 4, to which the pipe fittings 19 and 40 attach. The cap 21also has a lower surface 21b fitted with nipples 23 adjacent to a seriesof passageways that allow entry and egress of the gas stream: (i) inletpassageway 24 is L-shaped, is threadably connected to the inlet fitting19 at one end, and is also connected via central annulus 25 to interiorfilter media unit 26 concentric of vertical axis of symmetry 27; (ii) anoutlet passageway 28 that is bulbous over region 29 but is in fluidcontact with annular gathering region 30 that runs the full exterior ofthe filter media unit 26; the passageway 28 is then swedged over region31 (in L-shaped output form) at one end of bulbous region 29 forconnection to outlet fitting 40.

The cap 21 also has an annular side wall 21a, see FIG. 4, and inwardlyswedged at shoulder 32 and terminates at end 33. It is threadedtherebetween to engage with cylindrical canister 34. The canister 34includes a side wall 34a offset from the filter media unit 26 to formthe annular gathering region 30 previously described and in addition,has shoulders 35 and 36. The region between the shoulders 35, 36 and isthreaded to engage cap 21. Between shoulders 32 and 35 of the cap 21 andcanister 34, respectively, is grooved o/ring 37 to prevent gas leakageexterior of the filter assembly 20. The length of the engaging threadedportions of the cap 21 and canister 34 are constructed so that positivecontact exists only at the o-ring 37 and not at shoulders 33, 36.

Canister 34 also includes a bottom wall 34b. The bottom wall 34bincludes upwardly projecting nipples 38 concentric of a central annulus39. The latter attach to the filter housing 26. The purpose of thenipples 23 and central annulus 25 of the cap 21 as well as that of thenipples 38 and central annulus 39 of the canister 34 is to fixedlyreceive and hold the filter media unit 26 relative to the cap 21 andcanister 34.

Note that the direction of the gas stream at the interior of the filterassembly 20 is as taught by arrows 45, see FIG. 4. Such gas streamcannot pass directly from inlet passageway 24 to outlet passageway 28but is prevented to such flow due to the length of the annuli 25, 39.Thus the gas flow is in a radially expanding, sinusoidal pattern normalto the axis of symmetry 27 about horizontal axis A--A of the filtermedia unit 26. The pattern begins at the axis of symmetry 27 andprogresses through filter media unit 26, and ends exterior of the latterat annular gathering region 30. Thus the benzene is filtered from thestream.

FIG. 5 illustrates filter media unit 26 in more detail.

As shown, the filter media unit 26 includes end pieces 50a, 50b eachhaving a circular notch 51 at outer surface 52 into which nipples 23, 38of the cap 21 and canister 34, respectively, are received. Suchconstruction permits the end pieces 50a, 50b to take up firm surfacecontact with the cap 21 and the canister 34 as the cap 21 is threaded tothe latter.

Interior of the end pieces 50a, 50b are a series of concentric tubes 53,54, 55, 56 and 57 fitted into the notches 51 of the former. The tubes53-57 have side walls fitted with perforations 59. The side walls arenormal to the horizontal axis of symmetry A--A previously mentioned, thelatter being also normal to vertical axis of symmetry 27. Theperforations 59 permit gas flow in the sinusoidal-like, single passfiltering manner relative to axis A--A within the tubes 53-57 asindicated by arrows 45. As shown these arrows 45 begin near the verticalaxis of symmetry 27 and serpentine outwardly in sinusoidal fashionthrough the filter media unit 26.

Note that between the tubes 53 and 54; between tubes 54 and 55; betweentubes 55 and 56 and between tubes 56 and 57 are separate filter medium60, 61, 62 and 63 together forming a four-stage, single pass filteringmedia which in combination remove all benzene from the gas stream. Themedia 60-63 are each selected to remove benzene from the gas stream inprogressive fashion, viz., from microscopic to millimicrospic levels viasingle passage of the gas stream through each medium 60-63. However, themedia 60-63 do not filter the methane from the gas stream.

FILTER MEDIUM 60

In this regard, filter medium 60 is preferably pleated filter paperhaving the following characteristics. Pleated filter paper 60 is widelyavailable, performs impingement, absorption and absorption and is madeby conventional manufacturing processes including but not limited tomethods involving weaving of cellulose, wool, acrylic, rayon fibers intocorrugated sheet form. The tips and troughs of the corrugated pleatedfilter paper 60 of FIG. 5 are located in accordion fashion across andwithin the tubes 53, 54 but not in contact with the upper and lower endpieces 50a, 50b of the filter media unit. As shown in FIGS. 5 and 6, aseparate ring 64 is fitted in contact with each end piece 50a, 50b. Thering 64 of rectangular cross section, includes side wall 66 andterminating broad surface 67, that is compressively fitted in snugcontact with the upper and lower end piece 50a, 50b. As a result, thegas stream can circulate in the manner shown and pass through thepleated filter paper 60 in single pass fashion between inlet and outletperforations 59 associated therewith.

The density of paper 60 varies to provide filtering of benzene carriedon dust, rust, dirt, moisture and oil laden particles in a range of 40to 750 microns. It also retains both oils and moisture.

FILTER MEDIUM 61

In this regard, filter medium 61 is preferably silica gel in crystallineform located between tubes 54 and 55.

Silica gel 61 is a conventional drying and dehumidifying agent formed oramorphous silica in crystalline form for filtering and trapping benzenetransported in solution with water, in gaseous form as well as aboardsmaller diametered dirt and dust particles carrying benzene piggyback.The gel absorbs moisture within the gas stream but not oils and islocated between tubes 54 and 55. The medium 61 provides for singlepassage filtering operations only.

Calculations associated with the above are as follows:

AVERAGE NATURAL GAS USAGE

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

Assume the area between tubes 54, 55 is a function of a mean diameter of3 5/8 inches, a height of 5 inches and thickness of 0.875 inches, then

    Filter volume=52.5 cu. inches.

FILTER MEDIUM 62

Filter medium 62 is preferably open pore polyurethane foam for capturingbenzene in gaseous form. Filter medium 62 filters by impingement andadsorption and retains micro vapors and solid particulates includingoils and is located between tubes 55 and 56 for single pass filteringoperations. It has the following characteristics.

Shape: Cylindrical shape from sheet form Cellular Matrix Structure

Medium density--0.1 to 0.4 g/cu. cm matrix solid foam to gas insert

Porosity--0.14 to 0.41 (i.e. 70% to 90% open pore polyurethane)

Sample Period--2 months AT 100% Retention Well below breakthroughvolume, viz., the point at which concentration of solute in the columneffluent is half the concentration introduced into the column.

Volatility--Medium, See below

Preparation--Cut from foam sheets; air dry; install.

Pressure Drop--0.015 psi

Calculations associated with the above are as follows:

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

where: 0.714 mg/cu. meters is benzene

Hence: 295 cu. meter/month produces 210.14 mg/mo of benzene;

And: 54. cu. cm required to remove above am't of benzene

Filter volume=408.28 cu. cm via 5 inches height by 1/2 inches thicknessby 15.7 inches long;

Efficiency--700 cu. meters available

Change frequency=700/54=12.9 months

FILTER MEDIUM 63

Furthermore, filter medium 63 is preferably granular activated charcoallocated between tubes 56 and 57 for single pass filtering operations.

Granular activated charcoal is a conventional filtering medium, performsfiltering on liquids, gases and solid particulates down to 10 Angstromsin size (but does not retain water) by impingement and adsorption and isprepared by carbonization of raw materials such as wood, coconut shelland coal. It attracts and holds benzene irrespective of the mode oftransport such as liquid or gas alone or piggyback aboard dirt and dustparticles as well as with liquid plugs.

Physical properties:

    Surface Area=600 to 1050 cubic meters per gm

    Density=0.92 to 2.0 grams per cubic meter

    Effective size=0.8 to 1.5 mm

    Pore volume=0.6 to 1.7 cubic cm per gram

    Mean diameter=1.2 to 1.7 mm

    Sieve Size=No. 8 to No. 40 (U.S. Series)

    Iodine No.=650 to 1,000

Calculations associated with the above are as follows:

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

Assume the area between tubes 54, 55 is a function of a diameter of 7inches, a height of 5 inches and a thickness of 0.5 inches, then

    Filter volume=55. cu. inches;

    Density of GAC=0.30 oz./cu. in

    GAC Aviail=16.5 oz.

    Requirement to remove benzene associated with 295 cu. meters/month=0.944 oz.

    Change frequency=16.5/0.944=18.3 months

FIG. 7 illustrates alternative filter media unit 69 in detail.

As shown, the filter media unit 69 is similar to the filter media unit26 previously described, such filter media unit 69 having end pieces 70,71 fitted with inwardly facing notches 72 (relative to a horizontal axisof symmetry, not shown), and a series of concentric tubes 73, 74, 75, 76and 77 colinear with axis of symmetry 78. However, perforations 79 areprovided in side walls of tubes 73-77 to allow radial flow outwardlyfrom vertical axis of symmetry 78. Such construction does not permit thesinusoidal flow as previously mentioned, however. Instead, a gas streamflows as an annular mass through the filter media unit 69 beginning atthe axis of symmetry 78 and ending at the exterior of tube 77. Suchpattern is indicated by arrows S that are seen to expand outwardly fromthe axis of symmetry 78. The notches 72 aid in assembly as they take upfirm surface contact with the cap 21 and canister 27 of FIGS. 2, 3 and4, as the former and latter are threaded together.

Between the tubes 73 and 74; between tubes 74 and 75; between tubes 75and 76, and between tubes 76 and 77 are separate filter medium 80, 81,82 and 83 together forming a four-stage filtering media which incombination remove benzene from the gas stream. That is, the media 80,81, 82 and 83 are selected to remove all traces of benzene from the gasstream in the same order and similar filtering capacity as previouslydiscussed with reference to FIG. 5. In this regard, filter medium 80 ispleated paper, medium 81 is silica gel, medium 82 is open porepolyurethane foam and medium 83 is granular activated charcoal eachhaving characteristics as set forth above.

GUIDELINES FOR SELECTION OF FILTER MEDIA 60-63 & 80-83

Benzene exists in two states within the gas line network: primarily as aliquid and as a vapor. It is carried along because of the pulsation ofthe gas stream and surprisingly because of the gas phase transistioneffects created by the drive compressors of the gas system augmented bythe multiple outlet demands of the customers. But no matter how thebenzene is carried in the gas stream, the former are trapped within thefilter media 60-63 and 80-83 of the invention.

Gas phase transition is a little understood phenomenon in which variousdynamics due to changes in temperature, pressure, pipe size, flow ratesthat cause interaction between hazardous elements of the gas stream andvarious other elements in the network, such as pipe coatings, plug flows(aggregations of materials moving as a group) liquids and gaseous phasesof constituents of the natural gas stream. As a result, liquids andgases within the natural gas stream surprisingly change state. Theresulting gaseous phase may contain the hazardous elements which aretransported great distances.

As a vapor or liquid, the benzene is then carried along under like setsof circumstances described above.

PRESSURE CONDITIONS

As surface residue on solid particulates, benzene is carried along asfollows. At the well site, pressures in access of 2,000 psi occur. Suchpressure can be maintained until stepped down to about 1,000 psi, thenceto 60 psi and finally to about 1/2 psi at the user's residence orbusiness.

While filter media 60-63 and 80-83 are preferably as discussed above,substitutions can be made. For example, other types ofimpingement-adsorbing media could be used including silica sand,activated clay such as montomorillanite, natural zeolites composed ofhydrous calcium and aluminum silaceous materials, synthetic zeolitescalled molecular sieves such as sodium aluminum silicates, caitlin siltloam, dried corn husks, etc. Also, fluid baths, sonic collectors,electrostatic precipitators and thermal de-humidification devices couldalso be used.

Other impingement adsorbing media includes other packings such as can bewoven, coated or impregnated (such as with glycerol, glycerin, oils,glycol etc.). Other types of filters include membrane filter media foruse in natural gas environments generally above 100 psi in which thesolute is the force that helps perform the filtering, as well as specialfilters such as elongated, inter-latticed baffles that provideelectrostatic collection such as the HEPA filter (High EfficiencyParticle Accumulator filter, an acronym of The National Aeronautics andSpace Administration).

In some applications, fluid baths could be used, in which fluidsselected from a group that includes water, oil, alcohol, glycerol,glycerin, and glycol, could be used. Such use would require amodification to the canister 27 in order to provide a filteringoperation.

FURTHER METHOD ASPECTS

After installation has occurred, the filter system is an activefiltering state for benzene. That is to say, the valve 43 in the by-passnetwork 16 is closed and the valves 18 and 42 upstream and downstream ofthe filtering assembly 20 are opened.

When the filtering assembly 20 is to be re-charged, the valve 43 in theby-pass network 16 is opened so that gas is passing in parallel to thedownstream appliances (not shown). This assures ample gas supply beforethe filtering assembly 20 is deactivated. Such deactivation occurs whenthe valves 18 and 42 are closed. Then the canister 27 with the filtermedia 60-63 & 80-83 captured within its side wall 31, is removed fromcontact with cap 21, and the canister 27 and filter media 60-63 & 80-83are removed for transport to a waste station and disposal. A newcanister 27 with new filter media 60-63 or 80-83 are re-attached.

The above description contains several specific embodiments of theinvention. It is not intended that such be construed as limitations onthe scope of the invention, but merely as examples of preferredembodiments. Persons skilled in the art can envision other obviouspossible variations within the scope of the description. For example,the filter assembly 20 can be inserted in higher pressure lines of thegas transfer network, such as within the local utilities' pipingnetwork. Hence the scope of the invention is to be determined by theappended claims and their legal equivalents.

What is claimed is:
 1. A method of filtering, adjacent to an enduser-customer's residence or business in which at least a single gasappliance is located, a natural gas stream in which benzene has beenconcentrated at sufficient levels to be a health threat in a natural gasgathering and distributing network, comprising the steps of:(a)introducing the natural gas stream to a filter selected from a groupthat includes impingement, absorbing and adsorbing media whereby benzeneconcentrated in the gas stream at sufficient levels to be a healththreat by aperiodic loading of the natural gas within the gathering anddistributing network, are filtered from the gas stream and capturedirrespective of mode of transport, (b) passing the filtered natural gasstream to the customer's gas appliance wherein safe use of the energyassociated with the stream occurs, (c) periodically and safely removingthe filter of step (a) for disposing of captured benzene, (d) insertinga new filter in place of the removed filter of step (c).
 2. The methodof claim 1 in which said impingement, absorbing and adsorbing media ofstep (a) for filtering benzene, are selected from the group comprisingpleated filter paper, silica gel, open pore polyurethane foam andgranular activated charcoal.
 3. The method of claim 2 in which saidimpingement, absorbing and adsorbing media of step (a) comprises inseriatim, pleated filter paper, silica gel, open pore polyurethane foamand granular activated charcoal whereby benzene is removed from thenatural gas stream.
 4. The method of claim 1 in which step (a) isfurther characterized by aperiodic loading of in situ benzene being theresult of gas phase transition effects occurring within the natural gasgathering and distribution network.
 5. The method of claim 4 in whichstep (a) is further characterized by the natural gas gathering anddistributing network including compressor-driven equipment and multiplecustomer outlets connected to such equipment and by aperiodic loading ofin situ benzene within the natural gas gathering and distributingnetwork being the result of dampening effects of the compressor-drivenequipment and multiple customer outlet usage.
 6. The method of claim 5in which the natural gas gathering and distributing network includes gasmeters each connected to one of the outlets of the network and whereinsaid filtering occurs after such gas stream exits from the end user'sgas meter.
 7. The method of claim 1 in which said filtering occurs inthe natural gas gathering and distributing network.
 8. A method offiltering adjacent to an end-user-customer's residence or business inwhich at least a single gas appliance is located, a natural gas streamin which benzene has been concentrated at sufficient levels to be ahealth threat within a natural gas gathering and distributing networkconnected to the customer's gas appliance comprising the steps of:(a)introducing the natural gas stream to a filter selected from a groupthat includes impingement, absorbing and adsorbing media whereby benzeneconcentrated in the gas stream at sufficient levels to be a healththreat due to aperiodic loading within the natural gas gathering anddistributing network, is filtered from the gas stream and capturedirrespective of mode of transport, (b) passing the filtered natural gasstream to the customer's gas appliance wherein safe use of the energyassociated with the stream occurs.
 9. The method of claim 8 with theadditional steps of:(c) periodically and safely removing the filter ofstep (a) for disposing of captured benzene, (d) inserting a new filterin place of the removed filter of step (c).
 10. The method of claim 8 inwhich said impingement, absorbing and adsorbing media of step (a) forfiltering benzene is selected from the group comprising pleated filterpaper, silica gel, open pore polyurethane foam and granular activatedcharcoal.
 11. The method of claim 10 in which said impingement,absorbing and adsorbing media of step (a) comprises in seriatim, pleatedfilter paper, silica gel, open pore polyurethane foam and granularactivated charcoal whereby benzene is removed from the natural gasstream irrespective of mode of transport.
 12. The method of claim 8 inwhich step (a) is further characterized by aperiodic loading of in situbenzene being the result of gas phase transitional effects occuringwithin the natural gas gathering and distributing network.
 13. Themethod of claim 12 in which step (a) is further characterized by thenatural gas gathering and distributing network includingcompressor-driven equipment and multiple customer outlets operationallyconnected to such equipment and wherein step (a) is also characterizedby clumping of the situ benzene that is the result of dampening effectsproduced by the compressor-driven equipment and multiple customer outletusage within the natural gas gathering and distributing network.
 14. Themethod of claim 13 in which the natural gas gathering and distributingnetwork includes gas meters each connected to one of the outlets of thenetwork and wherein steps (a), (c) and (d) occur after the natural gasstream exits from the end user's gas meter.
 15. The method of claim 13in which steps (a), (c) and (d) occur within the natural gas gatheringand distribution network.